Depression and anxiety disorders are highly prevalent and associated with reduced quality of life for patients and enormous economic costs for society. Although effective treatments are available, a substantial number of patients fail to respond, and the time between disorder onset and treatment is typically long. The development of prevention programs therefore appears promising. The current project aims to prevent depression and anxiety by targeting excessive levels of worry and rumination, two important risk factors for emotional disorders. Participants will be selected on the basis of a high score on two validated questionnaires on worry and rumination. They will be randomly assigned to a rumination-focused cognitive-behavioral training delivered in a group format, a rumination-focused cognitive-behavioral training delivered via internet, or a no-training control condition. It is expected that both versions of the rumination-focused training will reduce symptoms of depression and anxiety, will reduce the incidence of major depressive episodes and generalized anxiety disorder, and will reduce symptom levels of other emotional disorders.